Multi-frequency power modulation for etching high aspect ratio features

ABSTRACT

A method of etching a substrate is described. The method includes disposing a substrate having a surface exposing a first material and a second material in a processing space of a plasma processing system, and performing a modulated plasma etching process to selectively remove the first material at a rate greater than removing the second material. The modulated plasma etching process includes a power modulation cycle composed of applying a first power modulation sequence to the plasma processing system, and applying a second power modulation sequence to the plasma processing system, the second power modulation sequence being different than the first power modulation sequence.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/341,840, filed on May 26, 2016, entitled“MULTI-FREQUENCY POWER MODULATION FOR ETCHING HIGH ASPECT RATIOFEATURES”, which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

The invention relates to a method for selectively etching one materialon a substrate relative to another material on the substrate usingplasma.

DESCRIPTION OF RELATED ART

The need to remain competitive in cost and performance in the productionof semiconductor devices has caused a continuous increase in devicedensity of integrated circuits. To accomplish higher integration andminiaturization in a semiconductor integrated circuit, miniaturizationof a circuit pattern formed on a semiconductor wafer must also beaccomplished.

Plasma etching is a standard technique used to manufacture semiconductorintegrated circuitry by transferring geometric shapes and patterns froma lithographic mask to underlying layers of a semiconductor wafer. Withincreasing aspect ratios and more complex materials, the need forstate-of-the-art etching processes that meet selectivity and profilecontrol requirement is becoming increasingly critical.

SUMMARY OF THE INVENTION

Embodiments of the invention relate to a method for selectively etchingone material on a substrate relative to another material on thesubstrate using plasma.

According to one embodiment, a method of etching a substrate isdescribed. The method includes disposing a substrate having a surfaceexposing a first material and a second material in a processing space ofa plasma processing system, and performing a modulated plasma etchingprocess to selectively remove the first material at a rate greater thanremoving the second material. The modulated plasma etching processincludes a power modulation cycle composed of applying a first powermodulation sequence to the plasma processing system, and applying asecond power modulation sequence to the plasma processing system, thesecond power modulation sequence being different than the first powermodulation sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a schematic representation of a patterningsequence on a substrate;

FIG. 2 provides a flow chart illustrating a method of etching asubstrate according to an embodiment;

FIG. 3 depicts a multi-frequency power modulation cycle according to anembodiment;

FIG. 4 shows a schematic representation of a plasma processing systemaccording to an embodiment;

FIG. 5 shows a schematic representation of a plasma processing systemaccording to another embodiment; and

FIG. 6 shows a schematic representation of a plasma processing systemaccording to yet another embodiment.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as a particulargeometry of a processing system, descriptions of various components andprocesses used therein. However, it should be understood that theinvention may be practiced in other embodiments that depart from thesespecific details.

Similarly, for purposes of explanation, specific numbers, materials, andconfigurations are set forth in order to provide a thoroughunderstanding of the invention. Nevertheless, the invention may bepracticed without specific details. Furthermore, it is understood thatthe various embodiments shown in the figures are illustrativerepresentations and are not necessarily drawn to scale.

Various operations will be described as multiple discrete operations inturn, in a manner that is most helpful in understanding the invention.However, the order of description should not be construed as to implythat these operations are necessarily order dependent. In particular,these operations need not be performed in the order of presentation.Operations described may be performed in a different order than thedescribed embodiment. Various additional operations may be performedand/or described operations may be omitted in additional embodiments.

“Substrate” as used herein generically refers to the object beingprocessed in accordance with the invention. The substrate may includeany material portion or structure of a device, particularly asemiconductor or other electronics device, and may, for example, be abase substrate structure, such as a semiconductor wafer or a layer on oroverlying a base substrate structure such as a thin film. The substratemay be a conventional silicon substrate or other bulk substratecomprising a layer of semiconductive material. As used herein, the term“bulk substrate” means and includes not only silicon wafers, but alsosilicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire(“SOS”) substrates and silicon-on-glass (“SOG”) substrates, epitaxiallayers of silicon on a base semiconductor foundation, and othersemiconductor or optoelectronic materials, such as silicon-germanium,germanium, gallium arsenide, gallium nitride, and indium phosphide. Thesubstrate may be doped or undoped. Thus, substrate is not intended to belimited to any particular base structure, underlying layer or overlyinglayer, patterned or un-patterned, but rather, is contemplated to includeany such layer or base structure, and any combination of layers and/orbase structures. The description below may reference particular types ofsubstrates, but this is for illustrative purposes only and notlimitation.

During pattern etching, a dry plasma etching process can be utilized,wherein plasma is formed from a process gas by coupling electromagnetic(EM) energy, such as radio frequency (RF) power, to the process gas inorder to heat electrons and cause subsequent ionization and dissociationof the atomic and/or molecular constituents of the process gas.Furthermore, the coupling of electromagnetic energy can be used tocontrol the energy level of charged species incident on the exposedsubstrate surface. Through control of various plasma properties,including charged specie density, charged specie flux, charged specieenergy, chemical flux, etc., a desired end result for the plasma etchingprocess can be achieved according to embodiments described herein. Inparticular, embodiments are provided that achieve target etchselectivity, profile control, and substrate charging control.

As described above, materials, typically employed in semiconductordevice manufacturing, are selectively removed relative to one anotherusing modulated plasma etching. Referring now to the drawings, whereinlike reference numerals designate identical or corresponding partsthroughout the several views, FIGS. 1A, 1B, 2, and 3 illustrate a methodfor etching a material on a microelectronic workpiece according to anembodiment. The method is pictorially illustrated in FIGS. 1A and 1B,and presented by way of a flow chart 200 in FIG. 2. As presented in FIG.2, the flow chart 200 begins in 212 with disposing a substrate 110having a surface exposing a first material (130) and a second material(140) in a processing space of a plasma processing system.

As shown in FIG. 1A, the substrate 110 can include a patterned layer 140overlying a film stack, including one or more layers 120, 130 to beetched or patterned. The patterned layer 140 can define an open featurepattern 150 overlying one or more additional layers. The substrate 110further includes device layers. The device layers can include any thinfilm or structure on the substrate into which a pattern is to betransferred, or a target material is to be removed.

Layers 130 and 140 can be any material utilized in the manufacture ofelectronic devices, including semiconductor devices, electro-mechanicaldevices, photovoltaic devices, etc. However, to selectively etch onelayer (e.g., layer 130 of a first material) relative to another layer(e.g., layer 140 of a second material), the material composition of thetwo layers is inherently different, such that each layer exhibits adifferent etch resistance when exposed to an etchant. Layers 130, 140can be organic or inorganic materials. Layers 130, 140 can besilicon-containing material, germanium-containing material,carbon-containing material, or metal-containing material. For example,silicon-containing materials can include amorphous silicon (a-Si),polycrystalline silicon (poly-Si), single crystal silicon, dopedsilicon, silicon oxide (SiOx), silicon nitride (SiNy), silicon carbide(SiCz), silicon oxynitride (SiOxNy), silicon oxycarbide (SiOxCz),silicon-germanium alloy (SixGe1-x), etc. Metal-containing materials caninclude a metal, a metal alloy, a transition metal (e.g., Ti, Ta, W, Ru,Co, Ni, Hf, etc.), transition metal oxide (e.g., titanium oxide (TiOx)),transition metal nitride (e.g., titanium nitride (TiNy)), carbides,chalcogenides, etc. Layers 130, 140 can include organic resists,anti-reflective coatings, or planarization layers, or silicon-containingresists, anti-reflective coatings, or planarization layers with varyingdegrees of silicon content. The above materials may be deposited usingvapor deposition techniques, or spin-on deposition techniques.

In FIG. 1B and in 214 of FIG. 2, the open feature pattern 150 overlyingone or more additional layers is extended into layer 130 by performing amodulated plasma etching process to selectively remove the firstmaterial (130) at a rate greater than removing the second material(140).

Referring now to FIG. 3, a modulated plasma etching process 300 isillustrated. In one embodiment, the modulated plasma etching process 300includes modulation of the radio frequency (RF) power delivered to asubstrate holder or susceptor upon which the substrate is positioned.The substrate holder can position the substrate facing an RF poweredelectrode, such as a capacitive coupling element or inductive couplingelement (to be described below). Alternatively, the substrate holder canposition the substrate facing a slotted plane antenna, wherein power ata microwave frequency is coupled to the slotted plane antenna, forexample. Exemplary systems are depicted in FIGS. 4 through 6. While themodulation of the RF power delivered to the substrate holder orsusceptor is described, it can alternatively be coupled to other powercoupling elements in the plasma processing system.

As shown in FIG. 3, the modulated plasma etching process 300 includes apower modulation cycle 310 that is composed of applying a first powermodulation sequence 312 to the plasma processing system, and applying asecond power modulation sequence 314 to the plasma processing system,the second power modulation sequence 314 being different than the firstpower modulation sequence 312.

As necessary to complete the modulated plasma etching process 300 tomeet target specifications, the power modulation cycle 310 is repeatedat least one more cycle, wherein each modulation cycle includes amodulation period. The power modulation cycle 310 can include a periodicmodulation cycle. As shown in FIG. 3, the power modulation cycle 310 canbe repeated at a power modulation frequency, represented as modulationperiod 311, for a determined modulation time period (equivalent to oneor more modulation periods), wherein the first power modulation sequence312 includes repeating a first sub-power modulation cycle 316 at a firstsub-power modulation frequency (or first sub-power modulation period).In particular, the first sub-power modulation cycle 316 includes:applying a radio frequency (RF) signal to the plasma processing systemat a first power level 320, and applying the RF signal to the plasmaprocessing system at a second power level 322, wherein the first andsecond power levels 320, 322 differ in value from one another.

In one example, the power modulation frequency is less than 1 kHz, andthe first sub-power modulation frequency is greater than or equal to 1kHz. In another example, the power modulation frequency is less than 500Hz, and the first sub-power modulation frequency is greater than orequal to 500 Hz. In yet another example, the power modulation frequencyis less than 100 Hz, and the first sub-power modulation frequency isgreater than or equal to 100 Hz. The threshold frequency can varydepending on the process.

As shown in FIG. 3, the first power level 320 exceeds the second powerlevel 322. And, in some embodiments, the second power level 322 is apower off state. In other embodiments, the RF signal is applied to theplasma processing system at an intermediate power level, wherein theintermediate power level resides at a value between the first and secondpower levels 320, 322.

The RF signal is applied at the first RF power level for a firstsub-time duration 324, and the RF signal is applied at the second RFpower level for a second sub-time duration 326. For example, the firstsub-time duration 324, during which the RF signal is applied at thefirst power level 320, can range from 10% to 90% of the time period ofthe first sub-power modulation cycle 316. In another example, the firstsub-time duration 324 can range from 40% to 60% of the time period ofthe first sub-power modulation cycle 316 (e.g., 50% duty cycle).

As shown in FIG. 3, the second power modulation sequence 314 can consistof a power off state. Alternatively, the second power modulationsequence 314 consists of applying the RF signal at a constant powerlevel.

In alternative embodiments (not shown), the second power modulationsequence 314 can include repeating a second sub-power modulation cycleat a second sub-power modulation frequency, wherein the second sub-powermodulation cycle includes: applying the radio frequency (RF) signal tothe plasma processing system at a third power level, and applying the RFsignal to the plasma processing system at a fourth power level, whereinthe third and fourth power levels differ in value from one another. Thesecond sub-power modulation frequency can be greater than or equal to 1kHz. The third power level can exceed the fourth power level, and thefourth power level can include a power off state.

The inventors surmise that the relatively high frequency nature of firstpower modulation sequence 312 reduces surface charging and improvesvertical profile of the feature being etched. And, the relatively lowfrequency nature of the power modulation cycle 310 enhances theexhausting of etch byproduct and reduces feature clogging.

During the modulated plasma etching process, at least one property ofthe modulation cycle may be adjusted. The at least one property mayinclude a power amplitude, a modulation frequency, a modulation dutycycle, a modulation waveform, or a modulation phase (relative to othermodulated properties, such as gas flow, source and/or bias power, etc.).

In one embodiment, the modulated plasma etching process may comprise aprocess parameter space that includes: a chamber pressure ranging up toabout 1000 mtorr (millitorr) (e.g., up to about 200 mtorr, or up toabout 50 to 150 mtorr), a halogen-containing gas flow rate ranging up toabout 2000 sccm (standard cubic centimeters per minute) (e.g., up toabout 1000 sccm, or about 1 sccm to about 200 sccm), a polymerizing gasflow rate ranging up to about 2000 sccm (e.g., up to about 1000 sccm, orabout 1 sccm to about 100 sccm), an optional noble gas (e.g., He or Ar)flow rate ranging up to about 2000 sccm (e.g., up to about 1000 sccm),an upper electrode/antenna power ranging up to about 2000-to-5000 W(watts) (e.g., up to about 1000 W, or up to about 600 W), and a lowerelectrode power ranging up to about 1000-to-2000 W (e.g., up to about600 W, or up to about 100 W, or up to 50 W). Also, the upperelectrode/anntenna frequency can range from about 0.1 MHz to about 3GHz. In addition, the lower electrode RF frequency can range from about0.1 MHz to about 100 MHz, e.g., about 2 MHz.

One or more of the methods for etching a substrate described above maybe performed utilizing a plasma processing system, such as the one thesystems described in FIGS. 4 through 6. However, the methods discussedare not to be limited in scope by this exemplary presentation. Themethod of etching a substrate according to various embodiments describedabove may be performed in other plasma processing systems notspecifically described below. Furthermore, various componentry describedin FIGS. 4 through 6 can be utilized, replaced with, or complemented byother componentry not described. While one or more RF or microwave powersources of various electromagnetic frequency are described, multiplesources above, below, or surrounding the substrate W are contemplated.

FIG. 4 is a schematic cross-sectional view of a microwave plasmaprocessing apparatus in accordance with embodiments herein. Themicrowave plasma processing apparatus can be configured to performplasma processing, such as plasma etching, plasma enhanced chemicalvapor deposition (PECVD), plasma enhanced atomic layer deposition(PEALD), etc., via surface wave plasma excitation at microwavefrequencies using, for example, a flat, plate-type slot antenna. Plasmaprocessing can be executed within processing chamber 401, which can be acylindrical vacuum chamber composed of a machined or cast metal, such asaluminum or stainless steel. The processing chamber 401 is electricallygrounded using, for example, ground wire 402. The processing chamber 401defines a processing vessel providing a process space PS for plasmageneration. An inner wall of the processing vessel can be coated with aprotective barrier, such as alumina, yttria, or other protectant.

At a lower, central area within the processing chamber 401, a susceptor412 (which can be disc-shaped) can serve as a mounting table on which,for example, a substrate W to be processed (such as a semiconductorwafer) can be mounted. Substrate W can be moved into the processingchamber 401 through loading/unloading port 437 and gate valve 427. Anelectrostatic chuck 436 is provided on a top surface of the susceptor412. Clamp electrode 435 is electrically connected to DC (directcurrent) power source 439. The electrostatic chuck 436 attracts thesubstrate W thereto via an electrostatic force generated when a DCvoltage from the DC power source 439 is applied to the clamp electrode435 so that substrate W is securely mounted on the susceptor 412.

A high-frequency power source 429 for applying a RF (radio frequency)bias is electrically connected to the susceptor 412, or bias electrodethrough an impedance matching unit 428 (to match impedance or minimizereflected power) and a power feeding rod 424. The high-frequency powersource 429 can output a high-frequency voltage in a range from, forexample, 0.2 MHz to 20 MHz, e.g., 13.56 MHz. Applying a high frequencybias power attracts ions, generated by the plasma in the processingchamber 401, to substrate W. Power source 429 can include a signalgenerator and amplifier for modulating the amplitude and power outputfrom the power source 429 according to the modulation cycle describedabove. A focus ring 438 is provided radially outside the electrostaticchuck 436 to surround the substrate W.

A coolant flow path 444 can extend, for example, in a circumferentialdirection, within susceptor 412 and can be configured to receivecirculated coolant to assist with controlling a processing temperatureof substrate W on the electrostatic chuck 436. Additionally, a heattransfer gas from a heat transfer gas supply unit (not illustrated) canbe supplied to a space between a top surface of the electrostatic chuck436 and a rear surface of the substrate W through a gas supply line 445.

An exhaust path 433 can be formed along an outer periphery of supportunit 414 and/or conductive support unit 416 and an inner wall of theprocessing chamber 401 in which an annular baffle plate 434 is attachedto the top or inlet of the exhaust path 433 and an exhaust port 432 (ormultiple exhaust ports), which is provided in a bottom portion of theexhaust path 433. A gas exhaust unit 430 is connected to each exhaustport 432 through gas exhaust line 431, which can have multiple exhaustlines. The gas exhaust unit 430 can include a vacuum pump such as aturbo molecular pump configured to decompress the plasma processingspace within the processing chamber 401 to a desired vacuum condition.

An upper portion of the microwave plasma processing apparatus will nowbe described. A dielectric window 457 is arranged to seal an upperportion of the processing chamber 401, through which electromagneticradiation at microwave frequencies can propagate to the process spacePS. A space just below the dielectric window 457 within the processingchamber 401 serves as a plasma generation space as process space PS. Thedielectric window 457 can be made of a microwave-permeable dielectricmaterial, such as quartz or ceramic, including aluminum oxide, and canhave a thickness of, for example, about 20 mm (millimeters) orsufficient thickness to mechanically resist the pressure differencebetween an interior of the processing chamber 401 and the ambientenvironment. The dielectric window 457 can be provided with a slot plate454 which can be a conductor attached to, or disposed on, a top surfaceof the dielectric window 457. The slot plate 454 can have a plurality ofslot pairs that are configured to irradiate microwaves distributedconcentrically in a rotationally symmetric arrangement, though othergeometric configurations can be used. On the slot plate 454, adielectric plate 456 can shorten the wavelength of microwaves propagatedinside the slot plate 454. The slot plate 454 is electromagneticallycoupled to a microwave transmission line 458. A slot antenna 455, whichcan be a flat plate-type slot antenna, for example, or a disc-shaped,radial line slot antenna, can include the slot plate 454, the dielectricplate 456, and an antenna rear plate (not shown) provided to be oppositeto the slot plate 454.

The microwave transmission line 458 is a line configured to propagate ortransmit electromagnetic waves at microwave frequencies or otherfrequencies, for example, microwaves of 2.45 GHz, which are output froma microwave generator 460 at a predetermined power level, to the slotantenna 455. The microwave transmission line 458 can include a waveguide462, a waveguide-coaxial line converter 464, and a coaxial line 466. Thewaveguide 462 can be, for example, a rectangular waveguide configured totransmit microwaves from the microwave generator 460 to thewaveguide-coaxial line converter 464. The coaxial line 466 extends fromthe waveguide-coaxial line converter 464 to the central portion of thetop of the processing chamber 401 and a terminal end of the coaxial line466 is coupled to the slot antenna 455 through the dielectric plate 456.An outer conductor 469 and an inner conductor 468 can define a space forwave transmission. A connector unit 479 is connected to the lower end ofthe inner conductor 468.

In addition, as electromagnetic waves propagate radially through thedielectric plate 456, the wavelength shortens, and the wave modetransitions to plane waves of circular polarization having twoorthogonal polarization components from each slot pair of the slotantenna 455 that are radiated toward the inside of the processingchamber 401. Process gas in the vicinity of the surface of thedielectric window 457 is then ionized by the electric fields of surfacewaves (microwave electric fields) propagated in the radial directionalong the surface of the dielectric window 457 and, as a result,high-density and low-electronic temperature plasma is generated.

The dielectric plate 456 can include a cooling jacket plate 442, whichcan serve as an antenna rear plate to cover a top of the processingchamber 401. The cooling jacket plate 442 can be configured to absorbheat (radiating) of dielectric loss, which is generated from thedielectric window 457 and the dielectric plate 456. To provide cooling,a coolant can be circulated in a flow path 443, and fed and removedthrough conduit 446 and conduit 448.

The microwave plasma processing apparatus can include two routes forprocess gas introduction. Upper gas introduction section 481 includes agas flow path provided in the dielectric window 457, and a side gasintroduction section 487 that includes a gas flow path provided in aside wall of the processing chamber 401, as a gas introduction mechanismconfigured to introduce a processing gas into the processing chamber401.

In the upper gas introduction section 481, a gas flow path 488 isprovided in the inner conductor 468 of the coaxial line 466 to extend inan axial direction through the inside of the inner conductor 468.Additionally, a first gas supply line 484 from a process gas supplysystem 480 is connected to the upper end of the inner conductor 468 andthe gas flow path 488 of the first gas supply line 484. The connectorunit 479 can have a plurality of internal flow paths which are bored andradially branched from a common inlet. The connector unit 479 can bemade of a conductor, and can be electrically grounded. The dielectricwindow 457 can be formed with inner flow paths connected to the terminalends of a branched gas supply paths such as for process gas tovertically pass through the dielectric window 457 to face the plasmageneration space within the processing chamber 401.

In the upper gas introduction section 481, a processing gas, which iscommunicated from the process gas supply system 480 at a predeterminedpressure (for example, an etching gas or a film-forming gas), flowsthrough the first gas supply line 484, the gas flow path 488 of thecoaxial line 466, and is ejected from each gas jet port 453 at theterminal end. A mass flow controller (MFC) 486 and corresponding valvecan be used for opening/closing and metering process gas flow in firstgas supply line 484.

In the upper gas introduction section 481, a processing gas, which iscommunicated from the process gas supply system 480 at a predeterminedpressure (for example, an etching gas or a film-forming gas), flowsthrough the first gas supply line 484, the gas flow path 488 of thecoaxial tube 466, and is ejected from each gas jet port 453 at theterminal end. A mass flow controller (MFC) 486 and corresponding valvecan be used for opening/closing and metering process gas flow in firstgas supply line 484.

The side gas introduction section 487 is placed at a position lower thana bottom surface of the dielectric window 457, and can include a bufferchamber 489 (manifold), sidewall gas jet ports 459, and a second gassupply line 485 extending from the process gas supply system 480 to thebuffer chamber 489. A mass flow controller 483 and corresponding valvecan be used for opening/closing and metering process gas flow in secondgas supply line 485. Process gas from side gas introduction section 487can be jetted in a substantially horizontal flow from the respectivesidewall gas jet ports 459 to be diffused in the process space PS.

Components of the plasma processing apparatus can be connected to, andcontrolled by, a control unit 450, which in turn can be connected to acorresponding storage unit 452 and user interface 451. Control unit 450can include a microcomputer configured to control operation of each ofthe components within the microwave plasma processing apparatus such as,for example, the gas exhaust unit 430, the high-frequency power source429, DC power source 439 for the electrostatic chuck 436, microwavegenerator 460, the upper gas introduction section 481, the side gasintroduction section 487, the process gas supply system 480, and a heattransfer gas supply unit (not illustrated) or the operations of theentire apparatus. Various plasma processing operations can be executedvia the user interface 451, and various plasma processing recipes andoperations can be stored in the storage unit 452. Accordingly, a givensubstrate can be processed within the plasma processing chamber withvarious microfabrication techniques.

FIG. 5 is a schematic cross-sectional view of a capacitively coupledplasma processing apparatus in accordance with embodiments herein. Thisapparatus can be used for multiple operations including ashing, etching,deposition, cleaning, plasma polymerization, plasma-enhanced chemicalvapor deposition (PECVD), and so forth. Plasma processing can beexecuted within processing chamber 501, which can be a vacuum chambercomposed of a metal, such as aluminum or stainless steel. The processingchamber 501 is grounded using, for example, a ground wire 502. Theprocessing chamber 501 defines a processing vessel providing a processspace PS for plasma generation. An inner wall of the processing vesselcan be coated with alumina, yttria, or other protectant. The processingvessel can be cylindrical in shape, or have other geometricconfigurations.

At a lower, central area within the processing chamber 501, a susceptor512 (which can be disc-shaped) can serve as a mounting table on which,for example, a substrate W to be processed (such as a semiconductorwafer) can be mounted. Substrate W can be moved into the processingchamber 501 through loading/unloading port 537 and gate valve 527.Susceptor 512 forms part of a lower electrode 520 (lower electrodeassembly) as an example of a second electrode acting as a mounting tablefor mounting substrate W thereon. Specifically, the susceptor 512 issupported on a susceptor support 515, which is provided at substantiallya central region of a bottom portion of processing chamber 501 via aninsulating plate 517. The susceptor support 515 can be cylindrical. Thesusceptor 512 can be formed of an aluminum alloy, for example.

Susceptor 512 can be provided with an electrostatic chuck 536 (as partof the lower electrode assembly) for holding the substrate W. Theelectrostatic chuck 536 is provided with a clamp electrode 535. Clampelectrode 535 is electrically connected to DC (direct current) powersource 539. The electrostatic chuck 536 attracts the substrate W theretovia an electrostatic force generated when a DC voltage from the DC powersource 539 is applied to the clamp electrode 535 so that substrate W issecurely mounted on the susceptor 512. A high-frequency power source 529for applying a RF (radio frequency) bias is electrically connected tothe susceptor 512, or bias electrode through an impedance matching unit528 (to match impedance or minimize reflected power). The high-frequencypower source 529 (a second power source) can output a high-frequencyvoltage in a range from, for example, 0.2 MHz to 20 MHz. Applying a highfrequency bias power attracts ions, generated by the plasma in theprocessing chamber 501, to substrate W. Power source 529 can include asignal generator and amplifier for modulating the amplitude and poweroutput from the power source 529 according to the modulation cycledescribed above. A focus ring 538 is provided radially outside theelectrostatic chuck 536 to surround the substrate W.

An inner wall member 519, which can be cylindrical and formed of quartz,for example, can be attached to the outer peripheral side of theelectrostatic chuck 536 and susceptor support 515. The susceptor support515 includes a coolant flow path 544 (for flowing chilled or heatedfluid). The coolant flow path 544 communicates with a chiller unit (notshown), installed outside the processing chamber 501. Coolant flow path544 is supplied with coolant (cooling or heating liquid, such as wateror dielectric fluid) circulating through corresponding lines.Accordingly, a temperature of the substrate W mounted on/above thesusceptor 512 can be accurately controlled. A gas supply line 545, whichpasses through the susceptor 512 and the susceptor support 515, isconfigured to supply heat transfer gas to an upper surface of theelectrostatic chuck 536. A heat transfer gas (also known as backsidegas), such as helium (He), can be supplied between the substrate W andthe electrostatic chuck 536 via the gas supply line 545 to assist inheating substrate W.

An exhaust path 533 can be formed along an outer periphery of inner wallmember 519 and an inner sidewall surface of the processing chamber 501.An exhaust port 532 (or multiple exhaust ports) is provided in a bottomportion of the exhaust path 533. A gas exhaust unit 530 is connected toeach exhaust port via gas exhaust line 531. The gas exhaust unit 530 caninclude a vacuum pump such as a turbo molecular pump configured todecompress the plasma processing space within the processing chamber 501to a desired vacuum condition. The gas exhaust unit 530 evacuates theinside of the processing chamber 501 to thereby depressurize an innerpressure thereof up to a desired degree of vacuum.

An upper electrode 570 (that is, an upper electrode assembly), is anexample of a first electrode that is positioned vertically above thelower electrode 520 to face the lower electrode 520 (as parallel plateelectrodes, for example). The plasma generation space, or process spacePS, is defined between the lower electrode 520 and the upper electrode570. The upper electrode 570 can include an inner upper electrode 571having a disk shape, for example, and an outer upper electrode 572having an annular shape, for example, that surrounds a periphery of theinner upper electrode 571. The inner upper electrode 571 also functionsas a processing gas inlet for injecting a specific amount of processinggas into the process space PS above substrate W mounted on the lowerelectrode 520. The upper electrode 570 thereby forms a shower head.

More specifically, the inner upper electrode 571 includes electrodeplate 575 (which is typically circular) having gas injection openings582. Inner upper electrode 571 also includes an electrode support 578detachably supporting an upper side of the electrode plate 575. Theelectrode support 578 can be formed in the shape of a disk havingsubstantially the same diameter as the electrode plate 575 (whenelectrode plate 575 is embodied as circular in shape). In alternativeembodiments, electrode plate 575 can be square, rectangular, polygonal,etc. The electrode plate 575 can be formed of a conductor orsemiconductor material, such as Si, SiC, doped Si, aluminum, and soforth. The electrode plate 575 can be integral with upper electrode 570,or detachably supported by electrode support 578 for convenience inreplacing a given plate after surface erosion. The upper electrode 570can also include a cooling plate or cooling mechanism (not shown) tocontrol temperature of the electrode plate 575.

The electrode support 578 can be formed of, e.g., aluminum, and caninclude a buffer chamber 589. Buffer chamber 589 is used for diffusingprocess gas and can define a disk-shaped space. Processing gas from aprocess gas supply system 580 supplies gas to the upper electrode 570.The process gas supply system 580 can be configured to supply aprocessing gas for performing specific processes, such as film-forming,etching, and the like, on the substrate W. The process gas supply system580 is connected with a gas supply line 584 forming a processing gassupply path. The gas supply line 584 is connected to the buffer chamber589 of the inner upper electrode 571. The processing gas can then movefrom the buffer chamber 589 to the gas injection openings 582 at a lowersurface thereof. A flow rate of processing gas introduced into thebuffer chamber 589 can be adjusted using a mass flow controller, forexample. Further, the processing gas introduced is uniformly dischargedfrom the gas injection openings 582 of the electrode plate 575(showerhead electrode) to the process space PS. The inner upperelectrode 571 then functions in part to provide a showerhead electrodeassembly.

A dielectric 576, having a ring shape, can be interposed between theinner upper electrode 571 and the outer upper electrode 572. Aninsulator 506, which can be a shield member having a ring shape andbeing formed of, e.g., alumina, is interposed between the outer upperelectrode 572 and an inner peripheral wall of the processing chamber 501in an air tight manner.

The outer upper electrode 572 is electrically connected with ahigh-frequency power source 560 (first high-frequency power source) viaa power feeder 565, an upper power feed rod 561, and a matching unit566. The high-frequency power source 560 can output a high-frequencyvoltage having a frequency of 40 MHz (megahertz) or higher (e.g., 60MHz), or can output a very high frequency (VHF) voltage having afrequency of 3-300 MHz. This power source can be referred to as the mainpower supply as compared to a bias power supply. The power feeder 565can be formed into a substantially cylindrical shape, for example,having an open lower surface. The power feeder 565 can be connected tothe outer upper electrode 572 at the lower end portion thereof. Thepower feeder 565 is electrically connected with the lower end portion ofthe upper power feed rod 561 at the center portion of an upper surfacethereof. The upper power feed rod 561 is connected to the output side ofthe matching unit 566 at the upper end portion thereof. The matchingunit 566 is connected to the high-frequency power source 560 and canmatch load impedance with the internal impedance of the high-frequencypower source 560. Note, however, that outer upper electrode 572 isoptional and embodiments can function with a single upper electrode.

Power feeder 565 can be covered on an outside thereof by a groundconductor 567, which can be cylindrical having a sidewall whose diameteris substantially the same as that of the processing chamber 501. Theground conductor 567 is connected to the upper portion of a sidewall ofthe processing chamber 501 at the lower end portion thereof. The upperpower feed rod 561 passes through a center portion of the upper surfaceof the ground conductor 567. An insulating member 564 is interposed atthe contact portion between the ground conductor 567 and the upper powerfeed rod 561.

The electrode support 578 is electrically connected with a lower powerfeed rod 563 on the upper surface thereof. The lower power feed rod 563is connected to the upper power feed rod 561 via a connector. The upperpower feed rod 561 and the lower power feed rod 563 form a power feedrod for supplying high-frequency electric power from the high-frequencypower source 560 to the upper electrode 570. A variable capacitor 562 isprovided in the lower power feed rod 563. By adjusting the capacitanceof the variable capacitor 562, when the high-frequency electric power isapplied from the high-frequency power source 560, the relative ratio ofan electric field strength formed directly under the outer upperelectrode 572 to an electric field strength formed directly under theinner upper electrode 571 can be adjusted. The inner upper electrode 571of the upper electrode 570 is electrically connected with a low passfilter (LPF) 591. The LPF 591 blocks or filters high frequencies fromthe high-frequency power source 560 while passing low frequencies fromthe high-frequency power source 529 to ground. A lower portion of thesystem, the susceptor 512, forming part of the lower electrode 520, iselectrically connected with a high pass filter (HPF) 592. The HPF 592passes high frequencies from the high-frequency power source 560 toground.

Components of the plasma processing apparatus can be connected to, andcontrolled by, a control unit 550, which in turn can be connected to acorresponding storage unit 552 and user interface 551. Various plasmaprocessing operations can be executed via the user interface 551, andvarious plasma processing recipes and operations can be stored instorage unit 552. Accordingly, a given substrate can be processed withinthe plasma processing chamber with various microfabrication techniques.In operation, the plasma processing apparatus uses the upper and lowerelectrodes to generate a plasma in the processing space PS. Thisgenerated plasma can then be used for processing a target substrate(such as substrate W or any material to be processed) in various typesof treatments such as plasma etching, chemical vapor deposition,treatment of glass material and treatment of large panels such asthin-film solar cells, other photovoltaic cells, and organic/inorganicplates for flat panel displays, etc.

High-frequency electric power in a range from about 3 MHz to 300 MHz, isapplied from the high-frequency power source 560 to the upper electrode570. A high-frequency electric field is generated between the upperelectrode 570 and the susceptor 512 or lower electrode. Processing gasdelivered to process space PS can then be ionized and dissociated toform a reactive plasma. A low frequency electric power in a range fromabout 0.2 MHz to 20 MHz can be applied from the high-frequency powersource 529 to the susceptor 512 forming the lower electrode. In otherwords, a dual or tri-frequency system can be used. As a result, ions inthe plasma are attracted toward the susceptor 512 with sufficient energyto anisotropically etch features via ion assistance. Note that forconvenience, FIG. 5 shows the high-frequency power source 560 supplyingpower to the upper electrode 570. In Alternative embodiments, thehigh-frequency power source 560 can be supplied to the lower electrode520. Thus, both main power (energizing power) and the bias power (ionacceleration power) can be supplied to the lower electrode.

FIG. 6 is a schematic cross-sectional view of an inductively coupledplasma processing apparatus in accordance with embodiments herein. Thisapparatus can be used for multiple operations including ashing, etching,deposition, cleaning, plasma polymerization, plasma-enhanced chemicalvapor deposition (PECVD), and so forth. Plasma processing can beexecuted within processing chamber 601, which can be a vacuum chambercomposed of a metal, such as aluminum or stainless steel. The processingchamber 601 is grounded using, for example, a ground wire 602. Theprocessing chamber 601 defines a processing vessel providing a processspace PS for plasma generation. An inner wall of the processing vesselcan be coated with alumina, yttria, or other protectant. The processingvessel can be cylindrical in shape, or have other geometricconfigurations.

At a lower, central area within the processing chamber 601, a susceptor612 (which can be disc-shaped) can serve as a mounting table on which,for example, a substrate W to be processed (such as a semiconductorwafer) can be mounted. Substrate W can be moved into the processingchamber 601 through loading/unloading port 637 and gate valve 627.Susceptor 612 forms part of a lower electrode 620 (lower electrodeassembly) as an example of a second electrode acting as a mounting tablefor mounting substrate W thereon. Specifically, the susceptor 612 issupported on a susceptor support 625, which is provided at substantiallya central region of a bottom portion of processing chamber 601. Thesusceptor support 625 can be cylindrical. The susceptor 612 can beformed of an aluminum alloy, for example.

Susceptor 612 can be provided with an electrostatic chuck 636 (as partof the lower electrode assembly) for holding the substrate W. Theelectrostatic chuck 636 is provided with a clamp electrode 635. Clampelectrode 635 is electrically connected to DC (direct current) powersource 639. The electrostatic chuck 636 attracts the substrate W theretovia an electrostatic force generated when a DC voltage from the DC powersource 639 is applied to the clamp electrode 635 so that substrate W issecurely mounted on the susceptor 612.

The susceptor 612 can include an insulating frame 613 and be supportedby susceptor support 625, which can include an elevation mechanism. Thesusceptor 612 can be vertically moved by the elevation mechanism duringloading and/or unloading of the substrate W. A bellows 626 can bedisposed between the insulating frame 613 and a bottom portion of theprocessing chamber 601 to surround support 625 as an airtight enclosure.Susceptor 612 can include a temperature sensor and a temperature controlmechanism, including a coolant flow path (for flowing chilled or heatedfluid), a heating unit such as a ceramic heater or the like (all notshown) that can be used to control a temperature of the substrate W. Thecoolant flow path communicates with a chiller unit (not shown),installed outside the processing chamber 601. Coolant flow path issupplied with coolant (cooling or heating liquid, such as water ordielectric fluid) circulating through corresponding lines. A focus ring(not shown), can be provided on an upper surface of the susceptor 612 tosurround the electrostatic chuck 636 and assist with directional ionbombardment.

A gas supply line 645, which passes through the susceptor 612, isconfigured to supply heat transfer gas to an upper surface of theelectrostatic chuck 636. A heat transfer gas (also known as backsidegas), such as helium (He) can be supplied between the substrate W andthe electrostatic chuck 636 via the gas supply line 645 to assist inheating substrate W.

A gas exhaust unit 630, including a vacuum pump and the like, can beconnected to a bottom portion of the processing chamber 601 through gasexhaust line 631. The gas exhaust unit 630 can include a vacuum pump,such as a turbo molecular pump, configured to decompress the plasmaprocessing space within the processing chamber 601 to a desired vacuumcondition during a given plasma processing operation.

The plasma processing apparatus can be partitioned into an antennachamber 603 and a processing chamber 601 by a window 655. Window 655 canbe a dielectric material, such as quartz, or a conductive material, suchas metal. For embodiments in which the window 655 is metal, the window655 can be electrically insulated from processing chamber 601, e.g.,insulators 606. In this example, the window 655 forms a ceiling of theprocessing chamber 601. In some embodiments, window 655 can be dividedinto multiple sections, with these sections optionally insulated fromeach other.

Provided between sidewall 604 of the antenna chamber 603 and sidewall607 of the processing chamber 601 is a support shelf 605 projectingtoward the inside of the processing apparatus. A support member 609serves to support window 655 and also functions as a shower housing forsupplying a processing gas. When the support member 609 serves as theshower housing, a gas channel 683, extending in a direction parallel toa working surface of a substrate W to be processed, is formed inside thesupport member 609 and communicates with gas injection openings 682 forinjecting process gas into the process space PS. A gas supply line 684is configured to be in communication with the gas channel 683. The gassupply line 684 defines a flow path through the ceiling of theprocessing chamber 601, and is connected to a process gas supply system680 including a processing gas supply source, a valve system and thecorresponding components. Accordingly, during plasma processing, a givenprocess gas can be injected into the process space PS.

In antenna chamber 603, a high-frequency antenna 662 (radio frequency)is disposed above the window 655 so as to face the window 655, and canbe spaced apart from the window 655 by a spacers 667 made of aninsulating material. High-frequency antenna 662 can be formed in aspiral shape or formed in other configurations.

During plasma processing, a high frequency power having a frequencyranging from a few MHz to hundreds of MHz, e.g., 13.56 MHz, to generatean inductive electric field can be supplied from a high-frequency powersource 660 to the high-frequency antenna 662 via power feed members 661.A matching unit 666 (impedance matching unit) can be connected tohigh-frequency power source 660. The high-frequency antenna 662 in thisexample can have corresponding power feed portion 664 and power feedportion 665 connected to the power feed members 661, as well asadditional power feed portions depending on a particular antennaconfiguration. Power feed portions can be arranged at similardiametrical distances and angular spacing. Antenna lines can extendoutwardly from power feed portion 664 and power feed portion 665 (orinwardly depending on antenna configuration) to an end portion ofantenna lines. End portions of antenna lines can be connected to thecapacitors 668, and the antenna lines are grounded via the capacitors668. Capacitors 668 can include one or more variable capacitors.

With a given substrate mounted within processing chamber 601, one ormore plasma processing operations can be executed. By applying highfrequency power to the high-frequency antenna 662, an inductive electricfield is generated in the processing chamber 601, and processing gassupplied from the gas injection openings 682 is excited to form plasmain the presence of electrons heated by the inductive electric field. Theplasma can then be used to process a given substrate, such as performingprocesses for etching, ashing, depositing, etc.

A high-frequency power source 629 for applying a RF (radio frequency)bias is electrically connected to the susceptor 612, or bias electrodethrough an impedance matching unit 628 (to match impedance or minimizereflected power). The high-frequency power source 629 (a second powersource) can output a high-frequency voltage in a range from, forexample, 0.2 MHz to 20 MHz, e.g., 3.2 MHz. Applying a high frequencybias power attracts ions, generated by the plasma in the processingchamber 601, to substrate W. Power source 629 can include a signalgenerator and amplifier for modulating the amplitude and power outputfrom the power source 629 according to the modulation cycle describedabove.

Components of the plasma processing apparatus can be connected to, andcontrolled by, a control unit 650, which in turn can be connected to acorresponding storage unit 652 and user interface 651. Various plasmaprocessing operations can be executed via the user interface 651, andvarious plasma processing recipes and operations can be stored instorage unit 652. Accordingly, a given substrate can be processed withinthe plasma processing chamber with various microfabrication techniques.

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

The invention claimed is:
 1. A method of etching, comprising: disposinga substrate having a surface exposing a first material and a secondmaterial in a processing space of a plasma processing system; performinga modulated plasma etching process to selectively remove the firstmaterial at a rate greater than removing the second material, themodulated plasma etching process comprising a power modulation cyclethat includes: applying a first power modulation sequence to the plasmaprocessing system, and applying a second power modulation sequence tothe plasma processing system, the second power modulation sequence beingdifferent than the first power modulation sequence; and repeating thepower modulation cycle at a power modulation frequency for a determinedmodulation time period, wherein the first power modulation sequenceincludes repeating a first sub-power modulation cycle at a firstsub-power modulation frequency, the first sub-power modulation cycleincluding: applying a radio frequency (RF) signal to the plasmaprocessing system at a first power level, and applying the RF signal tothe plasma processing system at a second power level, wherein the firstand second power levels differ in value from one another; wherein a timeperiod of the second power modulation sequence is greater than a timeperiod of the first sub-power modulation cycle.
 2. The method of claim1, wherein the power modulation frequency is less than 1 kHz.
 3. Themethod of claim 2, wherein the first sub-power modulation frequency isgreater than or equal to 1 kHz.
 4. The method of claim 1, wherein thefirst power level exceeds the second power level, and the step ofapplying the RF signal at the first power level occurs before the stepof applying the RF signal at the second power level.
 5. The method ofclaim 4, wherein the second power level is a power off state.
 6. Themethod of claim 1, wherein the first sub-power modulation cycle furtherincludes: applying the RF signal to the plasma processing system at anintermediate power level, wherein the intermediate power level residesat a value between the first and second power levels.
 7. The method ofclaim 6, wherein the first power level exceeds the second power level,and the step of applying the RF signal at the first power level occursbefore the step of applying the RF signal at the second power level. 8.The method of claim 7, wherein the second power level is a power offstate.
 9. The method of claim 1, wherein the applying the RF signal atthe first power level ranges from 10% to 90% of the time period of thefirst sub-power modulation cycle.
 10. The method of claim 1, wherein thesecond power modulation sequence consists of a power off state.
 11. Themethod of claim 1, wherein the second power modulation sequence consistsof applying the RF signal at a constant power level.
 12. The method ofclaim 1, wherein the second power modulation sequence includes repeatinga second sub-power modulation cycle at a second sub-power modulationfrequency, the second sub-power modulation cycle including: applying theradio frequency (RF) signal to the plasma processing system at a thirdpower level, and applying the RF signal to the plasma processing systemat a fourth power level, wherein the third and fourth power levelsdiffer in value from one another.
 13. The method of claim 12, whereinthe second sub-power modulation frequency is greater than or equal to 1kHz.
 14. The method of claim 12, wherein the third power level exceedsthe fourth power level.
 15. The method of claim 14, wherein the fourthpower level is a power off state.
 16. The method of claim 1, whereinperforming the power modulation cycle includes: generating a signalwaveform to execute the first and second power modulation sequences; andamplifying the RF signal according to the generated signal waveform. 17.The method of claim 1, wherein the RF signal is applied to a substrateholder upon which the substrate is positioned.
 18. The method of claim17, wherein the substrate holder positions the substrate facing an RFpowered electrode.
 19. The method of claim 17, wherein the substrateholder positions the substrate facing a slotted plane antenna.
 20. Themethod of claim 19, wherein power at a microwave frequency is coupled tothe slotted plane antenna.